Analysis of the Precipitation and Growth Processes of the Intermetallic Phases in an Fe-Ni Superalloy

The chapter characterizes wrought iron-base superalloys and comprises two main parts. The first describes the chemical composition, microstructure, and precipitation reactions in Fe-Ni, Ni-Fe, and Fe-Cr superalloys. The second part presents the influence of prolonged aging on the precipitation and growth processes in an Fe-Ni superalloy of A-286 type. The prepared specimens, after solution heat treatment at 980°C/2 h/water, were aged at temperatures of 715°C, 750°C, and 780°C with the holding time of 0.5-500 h. Transmission electron microscopy (TEM) and X-ray diffraction were used to examine their structures. It was found, that application of a single-stage aging causes precipitation processes of γ’ - Ni3(Al,Ti), η - Ni3Ti, β - NiTi, G - Ni16Ti6Si7, and σ - Cr0.46Mo0.40Si0.14 intermetallic phases, as well as the carbide M23C6 and boride M3B2. The main phase precipitating during alloy aging was the γ’- type intermetallic phase. It was found that the mean diameter of γ’ phase precipitates increases as a function of the cube root of aging time, which is consistent with the predictions based on the Lifshitz-Slyozow-Wagner (LSW) theory. The determined value of activation energy for the process of γ’ phase coagulation in the examined alloy was E = 297 kJ/mole

Ground state of two-component degenerate fermionic gases

We analyze the ground state of the two--component gas of trapped ultracold fermionic atoms. We neglect the forces between atoms in the same hyperfine state (the same component). For the case when the forces between distinguishable atoms (i.e., atoms in different hyperfine states) are repulsive (positive mutual scattering length), we find the existence of critical interaction strength above which one atomic fraction expels the other from the center of the trap. When atoms from different components attract each other (negative mutual scattering length) the ground state of the system dramatically changes its structure for strong enough attraction -- the Cooper pairs built of atoms in different hyperfine states appear.Comment: 10 pages, 14 figure

Radiative thermal conduction fronts

The discovery of the O VI interstellar absorption lines in our Galaxy by the Copernicus observatory was a turning point in our understanding of the Interstellar Medium (ISM). It implied the presence of widespread hot (approx. 10 to the 6th power K) gas in disk galaxies. The detection of highly ionized species in quasi-stellar objects' absorption spectra may be the first indirect observation of this hot phase in external disk galaxies. Previous efforts to understand extensive O VI absorption line data from our Galaxy were not very successful in locating the regions where this absorption originates. The location at interfaces between evaporating ISM clouds and hot gas was favored, but recent studies of steady-state conduction fronts in spherical clouds by Ballet, Arnaud, and Rothenflug (1986) and Bohringer and Hartquist (1987) rejected evaporative fronts as the absorption sites. Researchers report here on time-dependent nonequilibrium calculations of planar conductive fronts whose properties match well with observations, and suggest reasons for the difference between the researchers' results and the above. They included magnetic fields in additional models, not reported here, and the conclusions are not affected by their presence